488 Of Chimney Fireplaces. 



and more salubrious ; that they may be more equally 

 warmed, and more easily kept at any required tempera- 

 ture; that all draughts of cold air from the doors and 

 windows towards the fireplace, which are so fatal to 

 delicate constitutions, will be completely prevented ; 

 that in consequence of the air being equally warm all 

 over the room, or in all parts of it, it may be entirely 

 changed with the greatest facility, and the room com- 

 pletely ventilated when this air is become unfit for res- 

 piration, and this merely by throwing open for a mo- 

 ment a door opening into some passage from whence 

 fresh air may be had, and the upper part of a window ; 

 or by opening the upper part of one window and the 

 lower part of another. And as the operation of venti- 

 lating the room, even when it is done in the most com- 

 plete manner, will never require the door and window 

 to be open more than one minute, in this short time 

 the walls of the room will not be sensibly cooled, and 

 the fresh air which comes into the room will, in a very 

 few minutes, be so completely warmed by these walls, 

 that the temperature of the room, though the air in it 

 be perfectly changed, will be brought to be very nearly 

 the same as it was before the ventilation. 



Those who are acquainted with the principles of 

 pneumatics, and know why the warm air in a room 

 rushes out at an opening made for it at the top of a 

 window when colder air from without is permitted to 

 enter by the door or by any other opening situated 

 lower than the first, will see that it would be quite im- 

 possible to ventilate a room in the complete and expedi- 

 tious manner here described, where the air in a room is 

 partially warmed, or hardly warmed at all, and where 

 the walls of the room, remote from the fire, are con- 



